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Reverse binary representation of 8 (16) bit numbers
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(ns bitrev | |
(use clojure.test)) | |
;; http://dolzhenko.blogspot.ru/2012/12/blog-post.html | |
;; reverse binary representation of 8 bit number | |
;; reverse binary representation of 16 bit number | |
(defn reverse-8bit | |
"reverse 8 bit number" | |
[n] | |
;;; x = (x & 0x55) << 1 | (x & 0xaa) >> 1 | |
;;; reverse 1 bit and its neighbours | |
;;; x = (x & 0x33) << 2| (x & 0xcc) >> 2 | |
;;; reverse 2 bits and its neighbours | |
;;; x = (x & 0x0f) << 4 | (x & 0xf0) >> 4 | |
;;; reverse 2 bits and its neighbours | |
(let [x0 n | |
x1 (bit-or (bit-shift-left (bit-and x0 0x55) 1) | |
(bit-shift-right (bit-and x0 0xaa) 1)) | |
x2 (bit-or (bit-shift-left (bit-and x1 0x33) 2) | |
(bit-shift-right (bit-and x1 0xcc) 2)) | |
x4 (bit-or (bit-shift-left (bit-and x2 0x0f) 4) | |
(bit-shift-right (bit-and x2 0xf0) 4))] | |
x4)) | |
(defn reverse-16bit | |
"reverse 16 bit number" | |
[n] | |
(let [x0 n | |
x1 (bit-or (bit-shift-left (bit-and x0 0x5555) 1) | |
(bit-shift-right (bit-and x0 0xaaaa) 1)) | |
x2 (bit-or (bit-shift-left (bit-and x1 0x3333) 2) | |
(bit-shift-right (bit-and x1 0xcccc) 2)) | |
x4 (bit-or (bit-shift-left (bit-and x2 0x0f0f) 4) | |
(bit-shift-right (bit-and x2 0xf0f0) 4)) | |
x8 (bit-or (bit-shift-left (bit-and x4 0x00ff) 8) | |
(bit-shift-right (bit-and x4 0xff00) 8))] | |
x8)) | |
(deftest reverse-8bit-test | |
(are [n result] | |
(= result (reverse-8bit n)) | |
123 222 | |
0 0 | |
1 128 | |
3 192 | |
255 255 | |
0x33 0xcc | |
0xf0 0x0f)) | |
(deftest reverse-16bit-test | |
(are [n result] | |
(= result (reverse-16bit n)) | |
0 0 | |
1 0x8000 | |
3 0xc000 | |
0xff 0xff00 | |
0x193a 0x5c98)) |
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